A Southwest Airlines flight attendant was assaulted by a passenger and lost two teeth in the attack that took place last Sunday.

The incident shows an escalation of unruly behaviour by airline passengers and led the president of the flight attendants’ union to demand more federal air marshals on planes.

“I write to you today because we cannot tolerate our beloved cohorts being abused in such a manner, and because I am asking for your help and leadership in ending these travesties,” said the union president, Lyn Montgomery.

The incident happened during a flight from Sacramento to San Diego, California on Sunday morning.

Chris Mainz, Southwest spokesman said that the passenger repeatedly ignored flight attendant’s instructions and became verbally and physically abusive upon landing.

The flight attendant was taken to a hospital for treatment, and she was later released.

“I’ve been in the industry since 1992, and this is the worst ever,” Lyn Montgomery said in an interview. “People seem to be more angry. When they’re asked to do something, compliance seems to be more difficult,” she added.

All airlines train flight attendants to ease tense situations with unhappy passengers. Montgomery said those tactics are growing less effective and a small number of passengers are becoming bolder in challenging the authority of crew members.

According to Montgomery, flight attendants are concerned about Southwest’s plan to resume selling alcohol on board planes. Many recent cases involved passengers who were drinking.